The effect of construction activity on SPA waterfowl: a case study of the Abberton Reservoir Enhancement Scheme

• Main Author: Wallis, Kim Rachel
• Other Authors: Thompson, Stewart
• Format: Thesis
• Language: English
• Published: Oxford Brookes University 2017
• Subjects: Olor; Shoveler
• Online Access: https://doi.org/10.24384/dr0f-qw66; https://radar.brookes.ac.uk/radar/file/d5c21dd4-27f2-4fe3-aca2-11a0ce95a760/1/fulltext.pdf; https://radar.brookes.ac.uk/radar/file/d5c21dd4-27f2-4fe3-aca2-11a0ce95a760/1/appendices.pdf

Abberton Reservoir Essex, covering 4.85km2, is a water storage reservoir and is designated a Ramsar site, Special Protection Area (SPA) and Site of Special Scientific Interest (SSSI). In order to meet predicted increases in water demand, large scale construction works to raise the water level of the Main Section and consequently increase the storage capacity, were undertaken between 2010 and 2013. Construction work primarily involved breaking out 12km (7.4 miles) of concrete apron and perimeter road, raising the main dam by 3.2m and extensive shoreline re-profiling. This provided a unique and valuable opportunity to explore the effects of disturbance associated with construction activity on the spatial distribution of waterfowl. Nine species, all SPA interest features, were chosen as a basis for this study, the dabblers Anas strepera (Gadwall), A. clypeata (Shoveler), A. crecca (Teal) and A. penelope (Wigeon), divers Aythya fuligula (Tufted Duck), A. ferina (Pochard) and Fulica atra (Coot), the herbivorous Cygnus olor (Mute Swan) and the piscivorous Podicepts cristatus (Great Crested Grebe). As a consequence of both the reservoir’s importance to waterfowl and planning regulations, extensive waterfowl surveys were undertaken pre-construction and used to assess and predict the potential impacts arising from construction activity. Findings were used in the overall consideration of the development, with analysis determining appropriate mitigation measures which were subsequently incorporated into project design to ensure there would be no adverse impacts upon the integrity of the site. Waterfowl surveys continued throughout the four year construction period (2010 – 2013) and together with four years of pre-construction survey data (2006 – 2009), were used to make comparisons between the two periods. The spatial and temporal distribution analysis formed the first part of this research and provided a baseline from which to assess the effects of disturbance. The second part used a novel approach to assess the extent and magnitude of disturbance from construction activity on the SPA waterfowl species, with changes in distribution assessed against baseline data and in relation to environmental variables including water depth, percentage cover of macrophyte and distance to the shoreline. Finally, the success of mitigation measures to ensure no adverse impacts and overall enhancement of the site were investigated with respect to the use of created displacement habitat by waterfowl and in relation to measures to minimise construction disturbance. Numbers and distributions of all nine SPA species varied throughout the study period with numbers of waterfowl significantly increasing on the Main Section during construction. In contrast, although not directly subject to construction activity, the smaller Central Section suffered disturbance effects with the most significant decline seen for Tufted Duck. A general decline in over-wintering numbers of Tufted Duck was also observed. Findings show that the most important environmental variables determining distribution of the dabbling species was shallow water, with an increase in this habitat as a result of construction works, of particular benefit to Gadwall, Shoveler and Teal. Tufted Duck were found to be associated with deeper water and along with Pochard and Great Crested Grebe, were significantly related to areas containing high macrophyte cover. While results show some disturbance responses and evidence for a 200m zone of disturbance impact, the continued success and maintenance of site integrity during construction is attributed to the size of the reservoir complex (which in itself acted as a mitigating factor). The employed mitigation measures were also deemed successful and instrumental in reducing the extent and magnitude of disturbance. This is the first time research has related the extent and magnitude of construction activity to the spatial distribution of protected waterfowl species and provided an assessment against substantial baseline data. This research provides evidence for a sensitive and science based approach to development where extensive monitoring has enabled the much needed, but often lacking, reporting of mitigation in relation to development induced impacts.